The proposed research aims to determine the cellular mechanisms by which the synthesis of extracellular materials is regulated and the functions of extracellular materials in normal development processes. Cell cultures of chick chondrocytes and limb mesenchyme cells are being used as model systems to study feedback regulatory mechanisms involved in the control of matrix production and the steps leading to the onset of cartilage differentiation. The experimental approach involves the use of several environmental agents, such as conditioned medium from cartilage cell cultures and hyaluronic acid, as tools to study regulatory steps in the production of specific components of cartilage matrix. Some of the same materials present in cartilage matrix are also found in early embryos. Studies are underway on the possible functions of these extracellular materials during the early onset of cartilage differentiation.